Yes, you can always do multiple precision that way, but there is a performance hit, especially from those conditional branches. Maybe we need skip instructions such as the 7090 had.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Thomas David Rivers <riv...@dignus.com> Sent: Wednesday, September 9, 2020 8:35 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Support for 128-bit arithmetic - was: Re: PL/I support of vector instructions? Seymour J Metz wrote: >I was asking whether it supported vector instructions for FIXED, not for >FLOAT.; in particular, whether it supported FIXED BIN(127,0). > > >-- >Shmuel (Seymour J.) Metz >http://mason.gmu.edu/~smetz3 > > > You would not need vector instructions to support FIXED BIN(127,s) (quad-word scaled or unscaled integers if s is 0.) In fact, you could do it with 370 code (our C compiler happens to do that for __int128 and __uint128.) The problems come when consider conversions to-from other items... the definitions of those conversions are pretty straight-forward. The issue is examining all the conversion permutations for PL/I to make sure it's implemented... then there are the library I/O characteristics to consider (which are mostly handled by the conversion answers.) Will you need a PIC that handles this, is the maximum PIC length sufficent (_lots_ of base-10 digits in those things.) Do you need to read the values from a FILE, then you'll need CHAR -> FIXED BIN(127,s) conversion support... etc... Our C compiler, as well as GCC, gets around this by saying you can declare 128-bit integers, and do basic arithmetic with them - but the runtime library doesn't support them (so formating for printing, for example, is up-to-you.) That seems to handle the current uses for 128-bit integral arithmetic. Of course, C doesn't have scaled integers, making the problem even easier there. And - to drive the point home - let's consider this small snippet: __int128 foo(__int128 a, __int128 b) { return a + b; } which just adds 2 128-bit signed integers. This is the 370 code that is generated from our C compiler: * ******* End of Prologue * * L 15,0(0,1) * *** return a + b; LM 2,5,4(1) AL 5,32(0,1) BC 12,@@gen_label0 AL 4,@lit_147_0 BC 12,@@gen_label0 AL 3,@lit_147_0 BC 12,@@gen_label0 AL 2,@lit_147_0 @@gen_label0 DS 0H AL 4,28(0,1) BC 12,@@gen_label1 AL 3,@lit_147_0 BC 12,@@gen_label1 AL 2,@lit_147_0 @@gen_label1 DS 0H AL 3,24(0,1) BC 12,@@gen_label2 AL 2,@lit_147_0 @@gen_label2 DS 0H AL 2,20(0,1) STM 2,5,95(13) MVC 0(16,15),95(13) * *** } * * **** Start of Epilogue which is quite a lot! But - if you tell the compiler it can take advantage of more recent architectures (with the -march=z13 option) - that same snippet generates this (in 31-bit mode): * ******* End of Prologue * * L 15,0(0,1) * *** return a + b; LMG 2,3,4(1) ALG 3,28(0,1) ALCG 2,20(0,1) STMG 2,3,95(13) MVC 0(16,15),95(13) * *** } * * **** Start of Epilogue which is a better demonstration of how to do 128-bit arithmetic without vector instructions. - Dave R. - p.s. the return value is address via the first incoming parameter (0(0,1)) if that helps make sense of what's going on here. p.p.s. This facility would be available in LE mode too, so you _could_ compile C code with our compiler and link it with the IBM PL/I compiler to do your 128-bit arithmetic; with careful definitions of the C functions an PL/I EXTRNs. But, it might just be easier to write the PL/I PROCs to do the various arithmetic functions on 128-bit values held in structures - or maybe get really fancy and use the PL/I preprocessor to generate the code for the basic operations. -- riv...@dignus.com Work: (919) 676-0847 Get your mainframe programming tools at http://secure-web.cisco.com/1s90SO-UjL1WSVjVvb4AkJv2WPMJEueXQpFNLATgdwd3EHMXFE1iUBqoDQZLLvjq44lHvKMhIH0JF3bAw22v3WNj-8yUJAZe7Mgiw3mCCqbA5v1O3gHj_CucREhI5F4KIDLLqDUr33WO53oJQUzaLVnobKrb_3RgZorQHbo8AoYwavGFUJTobBrLageGchvdhaZUDBXFhLq5Yo9OmJSxZEUdiHJlqxHBfnJYnbhAANAAARmUTA9ujSfQOxhWM6jGJZAzQxVgEVjcGOr_sDboqRdSP-go0uNWVfVYGNqXARC_jfL0DQAAemO7MuXOB8PmLjHHe1AdIKVh48ZnxxTqJsDP8H0MiBZZCmOsOQ8zBM-eQWXzD7b8W0cJFYBTn8uSVGX5uQUhW1HZltx4z4_NhreVNI0zIiGvR490g_NhkVUZklaCY9WfOvYn3Irz-ADe3/http%3A%2F%2Fwww.dignus.com ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
